US3251537A - Heater for a diffusion pump - Google Patents

Description

y 7, 1966 e. H. BANCROFT ETAL 3,251,537

HEATER FOR A DIFFUSION PUMP Filed March 10. 1961 2 Sheets-Sheet 1 FIG. I

INVENTOR. GEORGE H. BANCROFT BQONALD STEVENSON ATTORNEY May 17, 1966 BANCROFT ETAL 3,251,537

HEATER FOR A DIFFUSION PUMP Filed March 10. 1961 2 Sheets-Sheet 2 N II I D l H q- ,1 l o o 09. l/ r m lu: I 8 i N P I I N] a N w a S I l l I O c ur r no m w" w 8 I m" xx 8 10 N m F I 3 i I\ l l m 0 o m N Q l l (0 (D O I m '1 Hil z N f 00 o I o Q INVENTOR. GEORGE H. BANCROFT BDONALD L. STEVENSON ATTORNEY United States Patent 3,251,537 HEATER FOR A DIFFUSION PUMP George H. Bancroft, Rochester, and Donald L. Stevenson,

Albion, N.Y., assignors to Consolidated Vacuum Corporation, Rochester, N.Y., a corporation of New York Filed Mar. 10, 1961, Ser. No. 94,727 12 Claims. (61. 230-101) The present invention relates to diffusion type vacuum pumps and, more particularly, to an improved heater for this type of pump.

Diffusion pumps for operational; high vacuums are well known. Such pumps operate on the principle that a liquid having relatively heavy molecules is vaporized in the pump by raising its temperature. The vapor -com prising heavy molecules is directed by suitable nozzles in a direction away from the region to be evacuated, towards a mechanical forepump. The accelerated molecules of vapor compress against molecules ahead of the nozzle,

forcing them toward the mechanical forepump and thereby reducing the pressure Within the evacuated region. The vapors are recondensed on a cool wall of the pump where the liquid is permitted to return to the bottom of the pump to be reheated and vaporized.

It has been the general practice heretofore to provide a reservoir of oil, for example at the bottom of the diffusion pump and to apply heat to the bottom of the diffusion pump by means of a flat electric heater attached to the bottom of the pump. The heat is transferred to the oil by conduction through the bottom wall of the pump. Thus the oil is caused to boil, producing vapors which rise in the pump wherein they are directed through orifices which produce the proper jets of heavy molecule vapors of the oil. In addition to being an inefficient means of transferring heat to the pump liquid, such known heating methods do not cause the liquid to boil uniformly. Local hot spots exist which produce greater boiling activity in certain portions of the liquid. The liquid does not release the vapors in a steady fashion. The result is erratic and ineflicient operation of the pump.

In U.S. Patent No. 2,943,783, which is assigned to the same 'assignee as the present invention there is described an improved heating means for a diffusion pump which supplies more heating uniformly through the volume of liquid. The heater described inthe above patent is particularly suitable for small diffusion pumps. In the U.S. Patent No. 2,943,784, which is assigned to the same assignee as the present invention, there is described a heating means for a relatively larger capacity pump than described in the Patent 2,943,783. This was accomplished in ,some measure by the difference of a plurality of the cartridge type of heaters described in the later patent. The present invention is particularly applicable to diffusion pumps of extremely large size wherein the use of a plurality say on the order of 40 to 80, cartridge type heaters are possible but relatively cumbersome in practice.

In brief, the present invention provides a diffusion pump in which at least one, but preferably a plurality of annular heating elements have their axes in coincidence with the central axis of the nozzle assembly for the pump. These heating elements project upwardly from the bottom of the pump and extendprimarily above the level of the 3,251,537 Patented May 17, 1966 rents both in the liquid and the vapor rising above the surface thereof.

A principal object of the present invention is to provide a novel and improved vapor operated diffusion pump.

Another object of the invention is to provide a novel heating device for a diffusion pump having relatively large size both in diameter and height.

For better understanding of the invention, reference should be made to the accompanying drawings wherein:

FIGURE 1 is a side elevational view, partially in section, of a diffusion pump incorporating the improved heater of the present invention;

FIGURE 2 is a perspective view of the heater assembly shown in FIGURE 1 and FIGURE 3 is a perspective view of the heaters from the heater assembly shown in FIGURE 2.

Referring to the form of the invention as shown in FIGURE 1, the numeral 11 indicates generally the housing of the diffusion pump which includes a hollow cylindrical casing 12 with an integral bottom wall 14. The bottom wall 14 may be brazed, Welded or otherwise secured to the bottom edge of the hollow cylindrical casing 12 in order to provide a hermetic seal therebetween.

The upper end of the pump is provided with a suitable inlet flange 16 to which a cooperating flange forming a part of the system being evacuated may be secured. The

inlet to the pump is provided with a centrally located opening 18 through the flange 16 and communicates with the interior of the housing 10. The discharge side of the pump is provided with a pipe 19, one end of which opens into the lower portion of the casing 12.

The interior of the pump includes a suitable nozzle assembly indicated generally at 20. The nozzle assembly may be of conventional design combining a hollow central sectional nozzle stack having overlapping sections forming annular downwardly directed orifices, such as indicated at 22, 24 and 16. Vapors rising in the center space of the nozzle assembly 20 are directed out of the respective orifices in downwardly directed nozzles. The lower cylindrical end 28 of the nozzle assembly 20 is radially spaced from a vapor confining member 30 which extends upwardly substantially to be overlapped by the lower end 28 as shown in FIGURE 1. An annular spacing 32 between the end 23 and the cylindrical wall 12 serves to permit the flow of condensed oil vapors to return to the pool of liquid in the bottom of the pump. The level of oil in the bottom of the pump is indicated by the numeral 34. The interior surface of the wall 12 condenses the vapors which are directed downwardly out of the nozzle orifices and the resulting oil droplets run down the Wall 12, through the annular spacing 32 and into the oil charge.

The heater assembly to which the present invention is particularly connected is located in the lower end of housing 10 for heating the liquid charges therein and generating vapors for operation of the pump nozzles. The bottom wall 14 is formed with a centrally disposed dome 36 which occupys a substantial area of the central portion of the bottom wall 14. The dome section 36 is formed with a vertical wall 38 which may be made integral with the dome 36 and the wall 14. Between the dome wall 38 and the cylindrical casing 12 of the housing 10, there is arranged a heater assembly comprising a pair of annular heater elements indicated generally by the reference numerals 39 and 40. The heater element 39 includes an annular, continuous metallic channel 42 formed integrally with the bottom wall 14 and defining an annular chamber 44 of rectangular transverse section. Similarly, the heater element 40 includes an annular, continuous metallic channel 46 formed integrally with the wall 14 and defining an annular chamber 47. The bottom wall 14 3 and the channels 42, 46 may be formed as a unit by casting, fabrication, welding or machined from stock.

The channels 42, 46 are concentrically arranged on the bottom wall 14 and have their axes in coincidence with the vertical axes of the dome 36 and the casing 12. An annular well 48 separates the inner channel 42 from the vertical wall 38 of the dome 36 and between the channels 42, 46 there is an annular spacing 50 which has a radial thickness approximately twice that of the well 48. This spacing 50 between the channels 42, 46 is divided by a cylindrical metallic member 52 which is seated'on the bottom wall 14 and extends vertically therefrom to a height equal to the height of the ridges above the bottom wall 14.

The spacing 50 is divided by the member 52 into two annular wells 54, 56 of equal radial thickness each of which is approximately equal to the radial thickness of the well 48. Within the well 54 there is provided a corrugated metallic element 58 which has the apexes of its peaks and valley in thermal contact with the inner channel 42 and t the member 52, respectively. Similarly a metallic corrugated element 60 is positionedbetween and in thermal contact with the channel 46 and the other side of the member 52. As will be indicated hereinafter, the elements 58, 60 serve as heat radiators for the pump fluid and to transfer heat from their respective channels to the member 56. To accomplish this it is desirable that the elements 58, 60 be tightly retained between the respective confining channels 42, 46 so that good heat conduction can be maintained through these metallic parts. If'practical, the peaks and valleys of the elements 58, 60 may be welded or brazed to their respective supporting structures, however, this may bediflicult to accomplish and frequent replacement may not warrant such permanent attachment.

Spaced from the outer surface of the channel 46 a dis-,

tance equal to the radial thickness of the well 48 and separated by aniannular well 61 is a cylindrical metallic member 62 which is similar to the member 52 and of equal height above the bottom wall 64. Within the well 61, between the member 62 and the outer surface of the outer channel 46 and secured therebetween as by a tight thermal contact fit, is a metallic corrugated element 64. This element performs the same functions as the elements 58, '60, that is, to radiate heat to the pump fluid and to conduct heat to the member 62. An annular well 65 separates the cylindrical member 62 and the wall of the casing 12 and serves to collect oil droplets which have condensed on the wall as previously mentioned.

Removably retained within the annular chamber 44 of the channel 42 is a metallic heater ring 64 having three circular tubular resistance heater rods 66 of equal radii embedded therein and arranged vertically axially of the ring. As shown in FIGURE 3, the ring 64 is split at one point and formed with a cutout section 68 and both ends of each of the heater rods 66 project through one end of the ring 64 at suitable points adjacent the cutout section 68. The ends of the heater rod 66 may be connected by conductors 70 to any suitable source of electric current (not shown).

A second metallic heater ring 72 is removably retained in the annular chamber 47 of the channel 46 and has the same configuration, exceptfor its large radius, as the ring 64 and includes three vertically spaced circular tubular resistance heater rods 74 embedded therein.

These rods 74 are also connected to the source of electric current as the rods 66. Preferably the heater rings 64, 72 are made from cast aluminum and their respective heater rods 66, 74 may be cast within the rings during casting thereof.

For eflicient heating, it is important that the coacting surfaces of the heater rings 64, 72 and the walls of their respective chambers 44, 47 be made as close as possible with the number of imperfections on these surfaces held to a minimum. As described so far, the heater element 39 comprises the channel 42, the heater ring 64, rods 66 and the fin arrangement or element 58 together with the cylindrical member 52. The heater element 40, in turn, comprises the channel 46, the heater ring 72, rods 74, and the fin arrangements or elements 6f), 64 together with the cooperating sides of the cylindrical members 52, 62, respectively.

It will be apparent after viewing FIGURE 1, that the heater rings 64, 72 are removable externally of the pump 10 from their respective channels from the bottom of the pump casing 16. These heater rings may be easily replaced or maintained without exposing the interior of the pump 10 to atmosphere or breaking any of the hermetic seals on the pump. In order to retain these heater rings in their normal positions shown in the drawing, there is provided a plurality of brackets 76, detachably secured to the bottom wall 14 by a pair of depending threaded lugs '78 secured to the wall 14. The brackets 76, only one of which will be described in detail, are suitably formed with apertures at their ends for receiving the lugs 78 and nuts 80 may be turned down on these lugs to retain the brackets ina radial arrangement relative to the bottom wall 14. Intermediate the ends of the brackets 76, there is formed threaded bores for retaining adjusting bolts 80, which are arranged on the brackets so as to be operable, when rotated, upon the heater rings 64, 72. These adjusting bolts may be driven upwardly as viewed in FIGURE 2 until contacts with the rings 64, 72 are made, whereupon further rotation of the bolts will serve to tighten the rings within their respective channels. It will be apparent that removal of the heater rings may be accomplished simply by removing the nuts associated with the lugs 73 and dropping the bracket 76 together with the adjusting bolts 80 from the bottom wall 14 of the pump.

In their arrangement on the bottom wall 14, each of the channels 42, 46 is continuous, that is, without any interrupting slots or other breaks in their configuration. The cylindrical members 52, 62 are similarly formed except that each is formed with an opening 82, 84 respectively, to permit pump fluid flow between both sides of the respective members (see FIGURE 2). These openings 82, 84 are in alignment along a common radius for the member 52, 62 and are arranged so that the openings face the adjacentportion of the bottom wall 14. Actually these openings are semi-circular in shape with the diameter of the opening contiguous to the surface of the wall 14.

The opening 82 is positioned immediately above a pas sageway 66 formed in the bottom wall 14. Similarly, another passageway 88 is formed above the opening 84. These passageways are connected to a common pipe 90 which serves as a conduit for the transmission of oil from a suitable external supply of pump fluid (not shown) to the wells, 54, 56, 61 and 65. A third passageway 92 connects the Well 43, adjacent the dome 36, with the pipe 90 for the transmission of fluid to this well.

As shown in the drawing, the normal level 34 of the pump fluid is maintained at approximately a quarter to a third the'distance below the plane of the top of the heater channels 42, 46. This level 34 isrnaintained at the same height for all of the Wells 48, 54, 56, 61 and 65 by virtue of the pipe W and openings 82, 84 which.

allows the fluid to seek a level that is common for the wells. In addition, the pipe 60 may be connected by an adapter 94 to any source of fluid supply which may be pumped through the pipes and into the various Wells. As

- previously mentioned, the'heater rings 64, 72 are formed In operation, the heater rods 66, 74 are energized to bring the heater rings 64, 72 and consequently, the channels 42, 46 respectively, up to a suitable temperature to vaporize the pump fluid.- During vaporization, heat is conducted from the channels to the corrugated elements 59, 60 and 64 and the metallic members 52, 62. Furthermore the individual plates 96 of the elements serve as .fins projecting from the respective heater channels for transmitting heat to the adjacent portions of the pump fluid. The portion of the pump fluid between any two adjacent fins or plates 96 and the included portion of the channel or cylindrical members '52, 62 as the case may be, is confined and since the cylindrical members are relatively cooler than the fins or channels, there is a tendency on the part of the members to remove heat from the pump fluid. By so confining these portions of the pump fluid and with the difference in heat between the channels and the cylindrical members, strong convection currents are produced in these portions of the fluid due to the combined heating of the heater channels and the cooling of vthe surrounding cylindrical members. These convection currents produce violent agitation of the pump fluid thereby decreasing the time any of the pump fluid is exposed to a heating surface. The result is more uniform heat distribution through the pump fluid and the elimination of localized hot spots which Would cause isolated areas of turbulence otherwise present in conventional heating arrangement. The present heater arrangement permits greater watts input to be supplied to the pump without decomposition of the pump fluid thereby adapting the pump for full operation in a minimum of time and for faster pumping speeds.

In the spaces directly above the level 34 and within the confines of the adjacent fins 96, the adjacent portion of the heater channels and the cylindrical members, all of which have vertical walls relative to the pump fluid, the vapors are further heated thus increasing the velocity of the rising vapor molecules and enhancing the pumping effect of the nozzle assembly 20. The height of those spaces may be. on the order of a fourth to a third of the height of the heater. elements 39, 40 and are available due to the fact that the heater elements of the present invention project upward through the pump fluid and beyond the surface thereof.

Although only two annular heater elements are illustrated, it will be apparent that additional annular elements may be arranged concentrically with elements 39 and 40, if desirable. In this event, the dome 36 would be made smaller to accommodate other elements centrally of the bottom wall 14. The dome 36 serves to minimize the quantity of pump fluid that is required for the operation of the pump and which would otherwise occupy space centrally of the bottom Wall. The dome extends above the level of the fluid and that portion thereof which is below this level is generally normal to the plane of the level surface. The portion'of the dome above the level may be of any shape such as spherical, as illustrated in the drawing. The dome at this portion may be conical, stepped or pyramidal or any other shape as long as the shape will allow condensed oil within the nozzle assembly to drain back to the boiler of the pump.

We claim:

1. A diffusion pump comprising an outer sealed casing closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and .open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one annular heater element having a wall projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater element having its axis in coincidence with the axis of said nozzle assembly, and a cylindrical wall concentrically spaced on each side of said heater element.

2. A diffusion pump comprising an outer sealed casing 6 closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one annular heater element having a wall projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater element having its axis in coincidence with the axis of said nozzle assembly, a cylindrical wall concentrically spaced on each side of said heater element, and a plurality of fins extending from said heater element between the same and at least one of said cylindrical walls.

3. A diffusion pump comprising an outer sealed casing closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; means for boiling the liquid continuously to generate vapor within the nozzle assembly including a plurality of annular heater elements having walls projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater elements being spaced from one another and having their axes in coincidence with the axis of said nozzle assembly, and cylindrical walls concentrically spaced on each side of each of said heater elements.

4. A diffusion pump comprising an outer sealed casing closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including a plurality of annular heater elements having walls projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater elements being spaced from one another and having their axes in coincidence with the axis of said nozzle assembly, cylindrical walls concentrically spaced on each side of each of said heater elements and a plurality of fins extending from said heater elements between the same and said cylindrical Walls.

5. A diflusion pump comprising an outer sealed casing and closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one annular heater element having a wall projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater element having its axis in coincidence with the axis of said nozzle assembly, and a cylindrical wall concentrically spaced on each side of said heater element for confining the liquid and vapors around said heater element, said cylindrical wall having a height such that part of the wall extends into the liquid and part above the level of the liquid.

6. A diffusion pump comprising an outer sealed casing and closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one annular heater element having a wall projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater element having its axis in coincidence with the axis of said nozzle assembly, a cylindrical wall concentrically spaced on each side of said heater element, and a plurality of fins extending from said heater element between the same and at least one of said cylindrical walls to form a compartmented region for the liquid charge, said cylindrical walls and the fins projecting above the bottom of the pump and extending vertically partly below and partly above the level of the liquid charge in the pump whereby the vapors from the boiling liquid in said compartmented region are additionallyheated by the heater element and fins as they rise within the nozzle assembly.

7. A diffusion pump comprising an outer sealed casing closed at its bottom and having input and output conduit connections thereto; a nozzle assembly-positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one heater element having an annular channel member projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof, and being positioned with its open side exposed externally of the pump, said channel member defining a chamber therein hermetically sealed relative to the interior of the pump and extending to a height above the surface of the liquid, an annular heater ring detachably mounted in said channel member, said heater ring being adapted for energization for heating the same and said channel member for vaporizing the liquid charge, said channel member having its axis in coincidence with the axis of said nozzle assembly, and cylindrical walls concentrically spaced on each side of each of said heater element.

8. A diffusion pump comprising an outer sealed casing closed at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one annular heater element having a wall projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof; said heater element having its axis in coincidence with the axis of said nozzle assembly, a cylindrical wall concentrically spaced on each side of said heater element, said cylindrical wall spaced on the inner side of the heater element being closed across its upper-most end by a dome portion for permitting condensed fluid vapors falling thereon to flow back to the liquid charge.

9. A diffusion pump comprising an outer sealed casing close-d at its bottom and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one heater element having an annular channel member projecting upwardly from the bottom of the casing through the liquid, and above the surface thereof, and being positioned with its open side exposed externally of the pump, said channel member defining a chamber therein hermetically sealed relative to the interior of the pump and extending to a height above the surface of the liquid, an annular heater ring detachably mounted in said channel member, at least one resistance heater rod embedded in said heater ring and detachable therewith, said heater rod being adapted for ener'gization for heating the same, said heater ring and said channel member for vaporizing the liquid charge, said channel member having its axis in coincidence with the axis of said nozzle assembly, and cylindrical walls concentrically spaced on each side of each of said heater element.

10. A diffusion pump comprising an outer sealed casing having input and output conduit connections thereto, a bottom wall in sealed engagement with the casing, a nozzle assembly positioned vertically in the casing and open at the lower end thereof, a liquid charge in the casing and retained therein by said bottom wall, said bottom wall being formed with a plurality of spaced apart upwardly projecting channels, each of said channels having a pair of walls projecting above the level of the liquid charge and having a top portion extending across the upper ends of said walls, said channel walls and top portions defining chambers therebetween hermetically sealed relative to the interior of the pump casing and having portions extending above the level of the liquid charge, a heater member detachably mounted within each of said chambers and being adapted for energization for heating said channel members, respectively, for vaporizing the liquid charge, a partition wall spaced on each side of each of said channel walls, anda plurality of fins extending from said channel walls to each of said partition walls to form compartmented regions for the liquid charge.

11. A diffusion pump comprising an outer sealed casing closed at its bottom by a wall and having input and output conduit connections thereto; a nozzle assembly positioned vertically in the casing and open at the lower end thereof; a liquid charge in the casing; and means for boiling the liquid continuously to generate vapor within the nozzle assembly including at least one curvilinear heater memberarranged around the axis of the nozzle assembly; said heater member projecting upwardly from the bottom of the casing through the liquid and above the surface thereof; curvilinear wall portions disposed on each side of said heater member, said heater member being corrugated and cooperable with the adjacent wall portions to form a multiplicity of small compartments for the liquid charge, the corrugated heater member and wall portions projecting above the bottom wall of the pump and extending vertically partly below and partly above the level of the liquid charge in the pump whereby the vapors from the boiling liquid in said compartments are additionally heated within the confines of said compartments above the level of the liquid.

12. A vaporizing and superheating element to be immersed within a liquid pool comprising a structure having a plurality of continuous curved surfaces defining void channels, said channels being arranged substantially normal to and extending above the surfaces of said pool, each of said surfaces being composed at least partially of a heat conducting material and means for supplying heat to said material.

References Cited by the Examiner UNITED STATES PATENTS 2,943,784 7/1960 Stevenson et a1 230-401 2,943,784 7/1960 Stevenson et a1. 230l01 MARK NEWMAN, Primary Examiner.

JOSEPH H. BRANSON, 1a., Examiner.

W. E. COLEMAN, Assistant Examiner.

Claims (1)

1. A DIFFUSION PUMP COMPRISING AN OUTER SEALED CASING CLOSED AT ITS BOTTOM AND HAVING INPUT AND OUTPUT CONDUIT CONNECTIONS THERETO; A NOZZLE ASSEMBLY POSITIONED VERTICALLY IN THE CASING AND OPEN AT THE LOWER END THEREOF; A LIQUID CHARGE IN THE CASING; AND MEANS FOR BOILING THE LIQUID CONTINUOUSLY TO GENERATE VAPOR WITHIN THE NOZZLE ASSEMBLY INCLUDING AT LEAST ONE ANNULAR HEATER ELEMENT HAVING A WALL PROJECTING UPWARDLOY FROM THE BOTTOM OF THE CASING THROUGH THE LIQUID, AND ABOVE THE SURFACE THEREOF; SAID HEATER ELEMENT HAVING ITS AXIS IN COINCIDENCE WITH THE AXIS OF SAID NOZZLE ASSEMBLY, AND A CYLINDRICAL WALL CONCENTRICALLY SPACED ON EACH SIDE OF SAID HEATER ELEMENT.

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